1. Field of the Invention
This invention pertains generally to hinges and more particularly to integral hinges of the snap action variety.
2. Prior Art
Snap action hinges in which a first member is movable into confronting relation with a second member are well known. For example, U.S. Pat. No. 3,289,877 issued to Wolfe and U.S. Pat. No. 3,720,979 issued to Krawagna both disclose snap action type hinges in which the hinge tends to hold itself in both the open and closed positions. Thus, FIGS. 5-9 of both Wolfe and Krawagna disclose a hinge having two members which are connected at their confronting edges by two arms extending therebetween. At some intermediate point the arms are thinned to provide a flexible web which accommodates movement of the hinge between the open and closed positions. Each of the members also has a portion which protrudes upwardly from between the arms, which portions are joined together along a second flexible web that is vertically spaced from the first web. The biasing forces acting at the second web tend to hold the hinge in the closed position once the members have been rotated through a point of unstable equilibrium with respect to each other. Similarly, these biasing forces tend to hold the hinge in the open position once the members have moved past the same point in the other direction. The disadvantage of both these hinges, however, is that the hinge members are joined together through two separate web portions. Thus, proper registration of the two hinge members upon closing is dependent upon the first and second web portions being properly aligned. Further, since the upstanding members which provide the biasing effect are connected together through a relatively thin juncture, which juncture is subjected to high stress each time the hinge is moved through the point of unstable equilibrium, these hinges are prone to failure with prolonged use.
U.S. Pat. No. 3,618,161 issued to Nozawa discloses another type of snap action hinge mechanism. In this hinge, however, the snap action is provided by rounded leg pieces as they slide along a flat surface through a point of unstable equilibrium. This hinge mechanism is impractical because it requires that the hinged object or the hinge itself be provided with a flat, rigid surface to accommodate sliding of the leg pieces. Moreover, movement of Nozawa's hinge between the open and closed positions is accompanied by vertical movement of the thin hinge axis through which the hinge members are joined. With prolonged use this may lead to hinge failure as well as difficulty in registering the leaves upon closing.
Other exemplary snap action hinges are disclosed in U.S. Pat. Nos. 3,512,227, 3,516,115, 3,594,852 and 3,676,896. None of these patents, however, disclose a snap action type hinge which avoids the disadvantages noted above.